It is known to recover synchronous data samples from an asynchronously oversampled analogue signal produced by a signal source for example a tape or disc drive, or a communications channel. It is known to use an FIR filter to compensate for variations in the spectral characteristics of the signal from the signal source. Prior proposals for doing that have either used complicated algorithms for the control systems controlling the recovery or used simpler algorithms which have other disadvantages. It is desirable to simplify the control system to allow the use of simpler algorithms whilst enhancing recovery of the data samples.